—Where do these magazines ______? —Put t
题型：选择题
问题：
— Where do these magazines ______?
—Put them back _______ they were.[ ]
A. go; where
B. lay; where
C. lie; to where
D. place; to which
题型：选择题
— Where do these magazines ______?
—Put them back _______ they were.[ ]
A. go; where
B. lay; where
C. lie; to where
D. place; to which
，两波源分别位于A、B处，
时的波形如图所示。当
时，M点的位移为 cm，N点的位移为 cm。